Known in the art is a light-reflection method for measuring transmission losses in optical fiber lightguides (U.S.S.R. Application No. 4,204,727, favorable Official Action as of May 30, 1988), comprising the steps of coupling a sounding radiation pulse into the lightguide under investigation, through an idle lightguide, whose length is half of that of the steady-state mode distribution for a given type of lightguide, measuring the energy, N.sub.1, of the pulse reflected from the output end face of the idle lightguide, measuring the energy, N.sub.2, of the pulse reflected from the output end face of the idle lightguide and the input end face of the lightguide under investigation, which end faces are spaced at a minimal distance from one another, measuring the energy, N.sub.3, of the pulse reflected from the output end face of the lightguide under investigation, determining transmission losses, .mu., per unit length of the lightguide under investigation. This method is viewed here as the prior art most closely related to the present invention in terms of its engineering essence.
A disadvantage of the known method of measuring losses lies in that it is impossible to make measurements at lightguide joints be that for two lightguides spliced without an air gap, or an arbitrary number of lightguides spliced with one another so as to accomodate minimal air gaps, or at those points where these lightguides are connected without an air gap.
It is a first object of the present invention to increase versatility by way of providing for the possibility of determining losses in any of the ith lightguides out of an arbitrary number of lightguides spliced with minimal air gaps.
It is a second object of the present invention to further increase versatility by way of determining optical transmission losses at the point of connection between an idle lightguide and the one under investigation, and consequently at the place of connection between any (i-1)th and ith lightguides spliced without an air gap.